The following case is far more remarkable, and seems at first quite
incredible; but it is the result of an astonishing number of
experiments made during many years on nine species of Verbascum, by so
good an observer and so hostile a witness, as Gartner: namely, that
yellow and white varieties of the same species of Verbascum when
intercrossed produce less seed, than do either coloured varieties when
fertilised with pollen from their own coloured flowers. Moreover, he
asserts that when yellow and white varieties of one species are
crossed with yellow and white varieties of a DISTINCT species, more
seed is produced by the crosses between the same coloured flowers,
than between those which are differently coloured. Yet these varieties
of Verbascum present no other difference besides the mere colour of
the flower; and one variety can sometimes be raised from the seed of
the other.
From observations which I have made on certain varieties of hollyhock,
I am inclined to suspect that they present analogous facts.
Kolreuter, whose accuracy has been confirmed by every subsequent
observer, has proved the remarkable fact, that one variety of the
common tobacco is more fertile, when crossed with a widely distinct
species, than are the other varieties. He experimentised on five
forms, which are commonly reputed to be varieties, and which he tested
by the severest trial, namely, by reciprocal crosses, and he found
their mongrel offspring perfectly fertile.
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